1. Field of the Invention
This invention relates to a device for providing audio biofeedback associated with the motion or tempo of a golf swing.
2. Background of the Invention
An important key to a reproducible swing, whether in golf, tennis, fishing, bowling, baseball, etc. is consistent tempo; once the player gets the correct swing for a given game situation, he/she must be able to repeat the swing in the same situation. A consistent tempo indicates that speed variations throughout the swing are repeated from swing to swing.
Perception of the tempo in a swing is generally very difficult in sports. An athlete's perception of fast and slow can vary from day to day, moment to moment, depending on mood, level of adrenaline, etc. Achieving consistent performance is further complicated by the fact that visual aids generally require diversion of attention away from more crucial focal points. Moreover, training is generally focused on tactile and visual perception by an observer other than the athlete and communicating problems with swing speed variation and tempo is difficult. Therefore finding a quantitative method of perceiving tempo, which does not interfere with the action of the swing, would be a useful athletic training/performance aid.
A natural pathway for perceiving tempo is through sound and music and has the advantage that the player can focus on his/her swing. Through extensive exposure to music, which is universal in all cultures, we are sensitized to the timing associated with tempo from an acoustic sensory perspective.
The instantaneous motions in a golf swing occur faster than one can consciously control, yet controlled speed and tempo are crucial to successful, reproducible performance. Further, muscle memory, which yields an unconscious coordination of muscle activity, can be learned by repetitive practice of a correct tempo. The auditory pathway is therefore an excellent mechanism for subconsciously providing swing tempo information without distracting the athlete.
A golf swing's tempo indicates the speed variation of the golf club as it traverses a circular route between the back swing, through impact with the ball and the follow through. Since a golf swing is dominated by motion in a circular path, the tempo of the swing is indicative of the time history, or tempo of the club's angular speed. Moreover, since the centripetal acceleration of a body traveling in a circular motion is a function of the angular velocity of the body, accelerometers mounted near a golf club head provide signals, which can be used to indicate tempo.
The centripetal acceleration at a particular point on a swinging club can be measured with an accelerometer at the point of interest and whose sensing axis is aligned along the axis of the shaft. In general, this centripetal acceleration, ac, can be used to yield an instantaneous measurement of the angular velocity squared of the club through the relation ac=ω2r, where ω is the angular velocity of the club shaft and r is the effective radius through which the accelerometer is moving.
The prior art appears to have recognized that measurement errors can occur due to the influence of gravity. The error signal, which can be confused with a desired centripetal acceleration signal, may be reduced or eliminated by making a differential measurement using two accelerometers located at different positions along the axis of the shaft; each accelerometer senses identical gravitational acceleration, but the centripetal acceleration scales as the effective radius of motion.
However, being able to fully benefit from accelerometers mounted on a golf club and the use of audio feedback has been somewhat elusive, but not for a lack of effort. For example, U.S. Pat. No. 6,261,102 describes converting the accelerometer output into an audio signal for biofeedback. With the axis of an accelerometer along the axis of the club, it measures the centripetal acceleration and from that value determines the square of the club's angular velocity. A signal proportional to the square of the club's angular velocity is then converted to frequency and fed to the person as an audio signal. Unfortunately, there is a perceived deficiency in its lack of compensating for the effects of gravity and tendency to create unpleasant “chirp like” sounds because of the large speed changes during a golf swing.
Two other relevant prior art patents suffer from similar deficiencies. Specifically, U.S. Pat. No. 5,233,544 to Kobayashi, while describing the use of multiple accelerometers along the golf club shaft, fails to recognize a potential for sound quality problems nor does he describe or suggest the use of multiple tones as provided in the present invention. Further, Kobayashi uses an angular velocity signal rather than an angular velocity squared signal and therefore does not provide for the sensitivity benefits of the velocity squared signal.
U.S. Pat. No. 5,694,340, to Kim, likewise describes the use multiple accelerometers to develop acceleration signals but fails to describe, suggest or appreciate the benefits of multiple accelerometers to cancel deleterious effects of gravity. Further, although Kim does use multiple frequencies, these different frequencies are used to distinguish between three axes and not to eliminate chirp or improving the tonal quality of the sound.
Accordingly, further advancements in the art are desirable. In particular, it would be desirable to provide a biofeedback system for a piece of athletic equipment, such as by way of example and not limitation, a golf club, that eliminates or at least reduces the effect of linear accelerations (not due to rotational motion) such as gravity that occur along the axis of the golf club and uses the angular velocity squared signal for increased sensitivity and improved sonification to produce pleasing sounds whose tonal composition and amplitude changes to indicate tempo. The present invention overcomes the foregoing deficiencies while achieving the objectives and advantages set forth herein.